A refurbished Robbins TBM broke through on the 1.6km long Tanner Ridge Tunnel, in the US, last month, marking completion of tunnelling on the Upper Diamond Fork section of the US$2.3bn Central Utah Project, designed to transfer water from the Colorado River Basin to the Great Basin.
The Obayashi/W W Clyde JV won the tender to build the US$29M Tanner Ridge Tunnel in March 2002 after the original project changed following the decision to abandon the last 10% of the Upper Diamond Fork Tunnel (see T&TNA, May 2002, p42), which had been under construction since October 2000 – also constructed by the Obayashi/W W Clyde JV.
Construction of the 7km long Upper Diamond Fork tunnel was halted in January 2002 when the Herrenknecht-refurbished Robbins TBM encountered hydrogen sulfide – laced geothermal water along a fault line, which began pouring into the tunnel at the rate of 3,000 gallons per minute – twice what was expected. Eventually the gas exceeded safety levels, and the acid started corroding the TBM. The tunnel was then sealed off with 7,000 bags of concrete, burying the TBM in the process.
The tunnel was only 880m away from the shaft connecting the final water outlet. The final section of the alignment was bypassed by the 3.8m diameter Tanner Ridge Tunnel, connected to the Upper Diamond Fork tunnel by a 2km long pipeline.
The system will be capable of delivering 200,000,000m3 of water each year by 2003. The client is the Central Utah Water Conservancy District, which employed Jacobs Associates, Camp Dresser McKee, and Golder Associates, as consultants.
